There are presently several general methods used to remove air borne particles from a gas/air stream, such as centrifugal separation, filtration, gravitational settling, wet scrubbing, and electrostatic precipitation.
In centrifugal separation, gravitational settling and electrostatic precipitation, suspended particles are subjected to forces created either mechanically or electrically that cause precipitation from the gas/air stream. The efficiency these methods depends upon the accuracy or balance of the forces causing the precipitation.
The filtration method places a filtration media directly in the gas/air stream to remove suspended particles.
In the wet scrubbing method, water or a liquid solution is used to cause particle precipitation. Droplets from a water spray in a wet scrubber collide with the air or gas stream, causing particle precipitation. Water is also introduced into electrostatic precipitators to assist in removing particles attached to the charged plates of the precipitators.
Water is also used to "wash" the gas/air stream; however, the efficiency of the devices depend mainly on the mechanical features, i.e., ducts, chambers, partitions, sprays, pressure, etc., that cause the gas/air stream to move within the designed architecture and permit the gas/air stream and the liquid to contact each other.
The degree of contact between the gas/air stream and the precipitating liquid determines the efficiency of particle precipitation from the stream into the liquid. The effectiveness of a liquid to cause suspended particles to precipitate is in the degree of contact that the liquid makes with the gas/air stream.
The cost to manufacture and maintain these systems over a long period of time to within designed standards can be considerable when used to service high volume requirements, such as those typically found in manufacturing facilities, building ventilation (HVAC) systems, etc.